Biomass selection and control for continuous flow granular/flocculent activated sludge processes

ABSTRACT

A continuous flow granular/flocculent sludge wastewater process selects for granule biomass capable of nitrogen and phosphorus removal and controls granule size and concentration of granular and flocculent sludge for optimal nutrient, organic, and solids removal in a smaller footprint. It includes anaerobic, anoxic, and aerobic process zones, a high soluble biodegradable COD loaded first reactor in anaerobic or anoxic zones, a granular sludge classifier with recycle of underflow granular sludge to the first reactor, a secondary clarifier to settle flocculent sludge and particulates and recycle of flocculent sludge from the secondary clarifier underflow to an aerobic process zone. Wasting of sludge from the two separate recycle lines controls the bioprocess flocculent and granular sludge concentrations and SRTs. Bypass around and recycle flow to the classifier to maintain desired flow under various influent flow conditions aid control of granule size. On/off mixer operation of anaerobic and anoxic reactors may be used.

This application claims benefit of provisional application No.62/718,313, filed Aug. 13, 2018.

BACKGROUND OF THE INVENTION

The application involves reactor process configurations and a granularsludge classifier process to control granular sludge size and relativefractions of granular and flocculent activated sludge in a combinedcontinuous flow wastewater treatment system for biological nutrientremoval.

The activated sludge process has been used since the early 1900s for thetreatment of domestic and industrial wastewater by microorganisms. Thebasic features of the traditional process are 1) mixing and aeration ofthe wastewater in a reactor with a flocculent mass containing activemicroorganisms and influent particulates, 2) a liquid/solids separationstep to separate and discharge the treated effluent from the flocculentmass, 3) wasting of excess mass produced from removal of wastewaterparticulates and biomass growth from the removal of influent substances,4) return of settled flocculent mass from an external liquid/solidsseparation step to the bioreactor or use of the settled flocculent massin the bioreactor for continuous or batch treatment of wastewater.

The process was first developed as a batch treatment process in whichthe above steps of biological contact, liquid/solids separation, andflocculent mass return are done in a single tank. Continuous flowversions of the process followed soon after and are the most commonversion used today. Continuous flow activated sludge treatment involvessingle or multiple bioreactors used in series and an externalliquid-solids separation step with recycle of the solids to thebioreactors. The process may involve the use of configurations withanaerobic, anoxic, and aerobic zones to meet treatment objectives.Gravity settling of solids in a clarifier is the most commonliquid-solids separation method. The clarifier also provides highremoval efficiency of suspended solids to produce a relatively cleareffluent low in suspended solids. Due to excess sludge production, awaste solids stream routinely removes solids from the system to controlthe bioreactor mixed liquor suspended solids (MLSS) concentration.

The traditional activated sludge process has a flocculent biomass thatin addition to consuming waste provides capture of particulate and finesolids to produce an effluent from the liquid/solids separation processthat is low total suspended solids (TSS). The flocculent biomass has avery diffused structure and a floc size commonly from 0.05-0.30 mm (FIG.1). Flocculent biomass is created by production of extracellularpolymeric substances during biomass growth which binds other bacteriaand also traps and contains colloidal and suspended particulates fromthe influent wastewater. Biomass growth in aerobic activated sludgeprocesses is the result of assimilation and oxidation of influentorganic substrate with a suitable electron acceptor such as oxygen,nitrate, or nitrite. Biomass growth can also occur from oxidation ofinorganic substrates such as ammonia, nitrite, reduced sulfur compounds,and reduced iron with a suitable electron acceptor. For the latter, thecarbon needed for biomass growth is derived from carbon dioxide.

The wastewater organic concentration is commonly measured in a batchbioassay using bacteria and is referred to as the BOD or biochemicaloxygen demand concentration. Treatment discharge standards require thatthe effluent BOD is below some specified value, typically 20 mg/L. Theeffluent BOD consists of soluble organic biodegradable substrate andbiodegradable colloidal and particulate solids. Treatment dischargestandards also require a low effluent total suspended solids (TSS) withvalues typically 20 mg/L. More stringent treatment requirements areoften required with effluent BOD and TSS concentrations 10 mg/L. Thephysical characteristics of flocculent activated sludge is effective incapturing free bacteria, and nondegraded colloidal and particulatesolids to meet permit limits for effluent TSS.

Different process tank configurations or batch treatment operation modesare also used in activated sludge processes to provide biologicalnitrogen removal and/or enhanced biological phosphorus removal (EBPR) toachieve low effluent concentrations of phosphorus and nitrogen(Tchobanoglous et al., 2014). Effluent nitrogen soluble inorganicspecies are ammonia (NH₃), nitrate (NO₃), and nitrite (NO₂). Theactivated sludge processes are designed with special configurations,including anaerobic, anoxic, and aerobic zones and operational methodsto select for bacteria with specialized metabolic capability importantfor nutrient removal. These processes include nitrification only, bothnitrification and denitrification (ND), and enhanced biologicalphosphorus removal (EBPR). Nitrification is the biological oxidation ofammonia (NH₃) to nitrite (NO₂) by one group of autotrophic bacteria andthen to nitrate (NO₃) by another group of autotrophic bacteria in thepresence of dissolved oxygen (DO). Nitrogen removal by denitrificationis done by heterotrophic bacteria that reduce NO₃/NO₂ to dinitrogen (N₂)gas during the oxidation of organic compounds in the absence of DO.Denitrification occurs in anoxic reactors. EBPR occurs in biologicaltreatment due to the growth and wasting of bacteria that store highconcentrations of phosphorus, which are referred to as phosphorusaccumulating organisms (PAOs). The growth of PAOs requires contact ofthe PAOs with influent wastewater under anaerobic conditions followed byanoxic and/or aerobic conditions. The anaerobic reactor does not receiveany significant amount of DO, NO₃ or NO₂. In the anaerobic contact zoneacetate and propionate volatile fatty acids (VFAs) from the influentwastewater or produced by organic solids fermentation in the anaerobiccontact zone are consumed by the PAOs and stored as polyhydroxyalkanoatecompounds. Stored polyphosphates in the PAOs provides energy needed bythe PAOs to take up carbon and convert to storage products. Phosphate isreleased from the PAOs to the reactor liquid during their polyphosphateuse in the anaerobic zone. The PAOs oxidize their carbon storageproducts using NO₃ or NO₂ in an anoxic zone which results in nitrogenconversion and nitrogen removal from the wastewater. PAOs oxidize theircarbon storage using oxygen in an aerobic zone. During their storedcarbon oxidation in anoxic or aerobic zones the PAOs create energy whichthey store in polyphosphate deposits by taking up phosphate from thereactor liquid. Wasting of excess PAO biomass results in phosphorusremoval from the system.

Nitrogen removal in continuous flow flocculent sludge systems have ananoxic process zone upstream of a nitrifying aerobic process zone. Theanoxic zone receives organic substrate for denitrification from influentwastewater feed or in flow from an anaerobic contact zone with PAOactivity. The anoxic reactor also receives NO₃/NO₂ in mixed liquorrecycle from the downstream aerobic nitrifying reactor. Denitrifyingbacteria oxidize the food in the anoxic reactor feed with reduction ofNO₃/NO₂ to nitrogen gas for nitrogen removal. PAOs from the EBPRanaerobic contact zone are also able to oxidize their carbon storagewith NO₃ or NO₂ in the anoxic zone to accomplish nitrogen removal.

More recently, it has been shown that activated sludge can be grown in amore compact approximate spherical self-formed biofilm layered structurein contrast to the more diffused flocculent activated sludge structure.These suspended biofilms are self-aggregating, do not require a carriermedia and are referred to as granular activated sludge. Their size maybe from 0.2 to 4.0 mm (Figdore et al., 2017). The structure of granularsludge is compared to flocculent sludge in FIG. 1. Due to the fact ofthe greater size, density, and smoother morphology, the granular sludgecan settle 5 to 30 times faster than flocculent sludge and can bethickened to a much higher concentration in a short time. A system highin granular sludge content has a 5-minute sludge volume index (SVI)approaching that of the 30-minute SVI or a SVI₅/SVI₃₀ ratio near 1.0,due to the discrete particles and fast settling. The biomassconcentration in a granular activated sludge treatment reactor can be 2to 3 times that for flocculent sludge to result in much greatertreatment ability or treatment capacity with less tank volume and lowerfootprint.

Granular biomass can be grown with ability for EBPR, nitrification, anddenitrification (Figdore et al., 2018a). The granules that contain PAOsare more versatile and, if of sufficient size, can provide simultaneousnitrification and denitrification (SND) for nitrogen removal in anaerobic zone in addition to phosphorus removal.

In contrast to flocculent sludge with its smaller and diffuse structure,granular sludge can have a layered spatial distribution of key types ofbacteria within different layers to provide unique phosphorus andnitrogen removal activity. The process configuration and classifier inthis application provides such type of granular growth due to the natureof the granular growth conditions and granular size selection. FIG. 1photomicrographs illustrate the magnitude of granule size and densityand a simple representation of the spatial distribution of bacteriainvolved in biological phosphorus and nitrogen removal. DO and NH₃ fromthe bulk liquid is taken up at the granule outer layers rich innitrifying bacteria. The NO₃ and NO₂ produced diffuses into the innercore of the granule that is rich in PAOs. The PAOs utilize the NO₃ andNO₂ for the oxidation of stored substrates with subsequent NO₃ and NO₂reduction to N₂. The soluble phosphorus in the bulk liquid is alsoremoved via diffusion and uptake by the PAOs. Due to the granule sizeall these reactions can occur in an aerated tank and thus the PAOgranules can provide simultaneous nitrification-denitrification (SND)for nitrogen removal and phosphorus removal in the same tank. Nitrogenremoval is accomplished in conventional flocculent sludge processesusing separate anoxic and aerobic reactors with internal recycle.Advantages of a granule sludge system for nutrient removal are 1) anefficient use of influent soluble BOD, also measured as solublebiodegradable chemical oxygen demand (COD), for both EBPR anddenitrification to accomplish phosphorus and nitrogen removal, and 2)denitrification in an aerobic zone which may eliminate the need for aseparate anoxic zone and internal recycle pumping for nitrogen removal.

An anaerobic contact zone with soluble food is a required processcondition to grow and sustain PAOs. When both granular sludge andflocculent sludge are recycled to an anaerobic contact zone the growthof granular sludge is inhibited. Flocculent sludge can also contain PAOsand can consume soluble biodegradable (bCOD) in the anaerobic contactzone faster than PAO-containing granular sludge because of diffusionlimitations for the large and denser granular biomass. Soluble bCOD fromthe bulk liquid must diffuse into the depth of the granules whichresults in a lower soluble BOD concentration with increasing depth.Thus, the overall rate of soluble bCOD uptake in g soluble bCOD/g VSS-his much slower for a granule than a floc because the uptake rate isproportional to the localized substrate concentration. The method inthis disclosure calls for an anaerobic first reactor contact withwastewater feed at a high soluble bCOD volumetric loading and recycle ofmostly granular biomass from the classifier as the first step, whichthus minimizes competition for food from the flocculent biomass andinstead allows more granular biomass growth and larger granules. Anothermethod using an anoxic contact zone in the same manner also favorsgrowth of granular biomass. Thus, the classifier that provides agranular sludge recycle to the high loaded first reactor works in tandemwith the first reactor to select for granular sludge growth of apreferred size and function.

A disadvantage of granular biomass is that the granular structure is notas effective as flocculent biomass in capturing colloidal and suspendedparticles contained in the wastewater. Results from a granular activatedsludge system consisting of biomass with over 90% granular sludge had anaverage effluent TSS concentration of 174 mg/L (Figdore et al., 2018b),which is well above wastewater treatment plant effluent permit TSSconcentration limits of 10-30 mg/L. Capture of colloidal and suspendedsolids by flocculent sludge and removal in liquid-solids separation isnecessary to minimize the effluent TSS concentration to meet effluentBOD and TSS treatment needs. A combined granular and flocculentactivated sludge system as describe in this disclosure can produce thenecessary effluent clarification needed to meet permit limits while alsoreducing treatment footprint requirement and providing nutrient removal.

Similar to the first flocculent activated sludge processes used, thedevelopment and application of granular activated sludge has been donewith sequencing batch reactors (SBRs). SBRs involve a batch feeding, areaction time, settling time, and effluent removal. The batch feedingtime comprises about 25% of the SBR processing time and thus multipleSBRs must be operated in synchronization or influent wastewater storageis needed.

Most biological wastewater treatment processes currently installed inthe United States and worldwide are continuous flow activated sludgeprocesses. SBRs have much different influent wastewater feedingarrangements and generally use deeper tanks than for continuous flowactivated sludge treatment systems. Process modifications that canconvert continuous flow flocculent activated sludge treatment systems toa combined granular/flocculent activated sludge system and maintain theexisting feeding and tank layout could provide many benefits includingnutrient removal and increased treatment capacity.

Most existing patents involving granular activated sludge for wastewatertreatment involve SBR technology. Others do not address the need forgrowth conditions that favor granular biomass growth with preferredtypes of bacteria over flocculent biomass growth to sustain a high levelof granular biomass in the activated sludge process and they also do notaddress the relative concentrations of granules and flocculent sludgepreferred for a combined granular/flocculent sludge process.

U.S. Pat. No. 6,566,119 relates to a sequencing batch reactor (SBR)operation producing aerobic granular activated sludge. A reactor isinoculated with aerobic microorganisms, fed a substrate under turbulentmixing conditions caused by sparging a gas containing oxygen, stoppingthe mixing for a time to allow settling of the aerobic microorganisms,and followed by removing liquid to empty the top part of the reactor andrepeating the batch feeding, aeration, settling, and effluent withdrawalcycle. The settling time is based on the height of the liquid remainingin the reactor in meters divided by a velocity of at least 5meters/hour.

U.S. Pat. No. 6,793,822 relates to an SBR operation producing aerobicbiogranules. The operation involves adding wastewater into a reactorcontaining an active biomass sludge, providing an oxygen-containing gasat a superficial upflow gas velocity greater than 0.25 cm/second toprovide oxygen for microbial uptake and to mix and suspend the biomass,initiating a period of nutrient starvation in the reactor willcontinuing to provide the oxygen-containing gas, allowing the formedaerobic granules to settle, and discharging and replacing at least aportion of the wastewater and subsequently repeating the operatingcycle. The patent claims did not specify a settling time, but thedescription specified settling times of 1 to 20 minutes. The nutrientstarvation time was estimated to be about 80% of the aeration period.

U.S. Pat. No. 7,273,553 relates to an SBR operation producing aerobicbiogranules that remove nitrogen and phosphorus compounds in addition toorganic substrates. The batch cycle consists of feeding wastewater intoa granular sludge bed in the bottom of the reactor under anaerobicconditions, aeration and mixing the reactor contents with anoxygen-containing gas, and a settling step to allow separation of theupper liquid from the activated sludge. The process descriptionspecifies that the wastewater can be introduced into the settled bedwithout fluidization of the bed or if mixing is used to contact thewastewater and settled sludge the bottom mixed volume be limited to 25%of the reactor volume. The upflow velocity during batch feeding is notgiven and a settling time of 3 min was given in a process example in thepatent description. Effluent withdrawal was given at 50% of the reactorheight in the example but no specifications on the location of theeffluent removal or effluent removal during feeding (as is now done inthe process application) was given in the claims or example. Thisprocess operation provides an environment that favors the growth ofgranules containing PAOs as described above due to the feeding ofwastewater to an anaerobic zone with settled granules and subsequentlyaerobic nitrification and denitrification reactions.

U.S. Pat. No. 8,409,440 describes another form of an SBR process usingtwo compartments and with conditions to favor growth of granular biomasswith phosphorus and nitrogen removal ability. Two reactor compartmentsthat communicate with each other at the bottom are used. Batch chargingof wastewater to the system is done by using a vacuum in the head spaceof compartment 1, which allows the intake of a batch feed withoutdisturbing a settled granular sludge bed in compartment 2. The next stepin the cycle is to open compartment 1 to atmospheric pressure, whichresults in compartment 2 receiving the batch feed from compartment 1.The feed is distributed across the reactor bottom area of compartment 2to contact and fluidize the granular bed with the wastewater underanaerobic conditions. A series of batch feedings may follow. This isthen followed by aeration and settling steps. A settling time of 5minutes before effluent decanting was given in the patent description.

Sequencing batch reactor treatment processes that accomplish biologicalnutrient removal with a granular activated sludge have been identified.However most biological treatment processes for wastewater treatment arecontinuously fed systems with external clarifiers. The continuously-fedsystems are preferred over SBR systems for moderate and larger sizeplants in view of economics, space requirements, and operationalcomplexity. Conversion of existing continuously-fed systems to SBRsystems for granular sludge selection may be difficult and noteconomically attractive in most cases in view of the arrangement of theexisting tanks and the plant piping and hydraulics. The ability toconvert existing facilities or design new facilities that developgranular activated sludge with biological nutrient removal is attractivein terms of the potential increase in plant capability and capacityprovided by the dense granular biomass.

U.S. Pat. No. 5,985,150 relates to an aerobic activated sludge reactorwith two zones and a separator in the second zone for continuous-flowtreatment with granules. Oxygen containing gas in the second zonecreates a recirculation of reactor contents between the second and firstzones with downward velocity in the first zone created by the rising gasand higher liquid elevation in the second zone. The first zone alsoreceives influent wastewater. Effluent is removed in a three-phaseseparator including release of gas released from the recirculation flowfrom the second zone to the first zone. The recirculated flow enters achamber at the top of the first zone. Water flows out of the chamber andthen upward through plate settlers at a velocity to allow the granularactivated sludge to settle back to the first zone for recirculation. Thetreated effluent exits via the plate settler. An example of the processshows an upflow velocity of 14 meter/hour in the plate separator, whichwould carry out the lighter flocculent sludge and allow granular sludgewith its higher settling velocity to be retained in the reactor.

U.S. Pat. No. 5,985,150 had no anaerobic contact zone to develop PAOgranules and granules capable of SND, and no conditions to wash outflocculent sludge, and thus high effluent total suspended solids (TSS)would be expected for treatment of domestic and industrial wastewaters.

U.S. Pat. No. 7,060,185 relates to an apparatus for treating sewageusing granulated sludge. The system has three tanks in series withrecirculating flow from the last tank to the first tank. The first tankis described as an anaerobic granulation tank, the second in series isan indirect aeration tank and the third in series is referred to as anaerobic granulation tank. The anaerobic granulation tank receives flowat the bottom of the tank made up of influent wastewater and recyclefrom the aerobic granulation tank. The recycle from the aerobicgranulation tank contains nitrate/nitrite due to the ammonia oxidationin the aerobic granulation tank. Phosphorus removing organisms containedin the granulated sludge use the recycled nitrate/nitrite for electronacceptors. The tank also contains an agitator and an upflow velocity ofliquid results in a supernatant without granules that flows to theindirect aeration tank. Oxygen is dissolved at super saturatedconditions in the indirect aeration tank. Flow from the indirectaeration tank provides dissolved oxygen for the final aerobicgranulation tank. This flow is distributed in the bottom of the aerobicgranulation tank and an agitator in the bed is also present. The upflowvelocity carries supernatant without granules with part of it beingdischarged as treated effluent and the rest as recirculation flow to theanaerobic granulation tank. The liquid upflow velocity is claimed to be1.3 to 1.7 meters/hour which would not be sufficient to suspendgranules.

U.S. Pat. No. 7,060,185 involves indirect aeration which requires muchhigher energy than that used by conventional activated sludge aerationmethods and involves a very high recycle of flow for aeration. Theadvantage claimed for the method is that it provides higher efficiencyin removing nitrogen and phosphorus due to the microorganism selection,but does not claim to provide a higher biomass concentration in thereactors due to granular growth to increase reactor capacity. It is alsoa very complex system that cannot be easily adapted to existingcontinuous flow activated sludge systems.

U.S. Pat. No. 7,459,076 relates to a flow-through aerobic granulatorreactor, which is intended to process continuous wastewater flow, selectand sustain aerobic granular biomass, and accomplish biological nitrogenand phosphorus removal. The reactor may consist of three or four zones.The three-zone system has an anaerobic zone in which influent wastewaterflows through a settled granular sludge bed, an aerobic or operationallyan aerobic/anoxic zone, and a settling zone. The four-zone system has ananaerobic zone in which influent wastewater flows through a settledgranular sludge bed, an anoxic zone that receives recirculated biomassfrom the aerobic zone and effluent from the anaerobic zone, and asettling zone. Airlift pumps periodically transfer solids from theanaerobic zone to the aerobic or anoxic zones. The settling zone, whichhas a series of settling plates, receives effluent flow at a high upwardvelocity (4 meters/hour or greater) to wash out lighter flocculentbiomass with settling of the separated granules directed to theanaerobic zone.

U.S. Pat. No. 7,459,076 selects for only granular sludge and washes outflocculent sludge entirely. It provides influent feeding only throughsettled sludge. It may also be energy inefficient due to the need todepend on sufficient aeration air lift to accomplish recirculation offlow from the aerobic to anoxic zone. It also requires multiple air liftpumps to move granules from the anaerobic to the aerobic zone. Itsphysical arrangement of the zones would not be adaptable to manyexisting activated sludge systems.

U.S. Pat. No. 9,242,882 relates to a method used to waste excess sludgeand select for heavier settling solids in an activated sludge process toimprove the activated sludge settling characteristics as measured by theSludge Volume Index (SVI). This is accomplished by passing the wastesludge stream through some type of gravimetric separator with thelighter solids wasted from the biological treatment system and theheavier solids returned to the biological process. The patent indicatesthat the gravimetric separator could be any process that selects andretains solids with superior settling properties. The patent describesthe separator as receiving the process stream from the biologicalreactor, returning a stream from the separator with the solids withsuperior settling properties to the biological process, and wasting theremaining solids stream from the separator for sludge processing. Analternative approach described is feeding a stream from the bottom ofthe secondary effluent clarifier to the separator and feeding theseparated heavier solids to the biological process and wasting thestream with the lighter solids. The process description states that thegravimetric separator devices include a settling tank, a settlingcolumn, cyclone, hydrocyclone, and centrifuge as examples of apparatusin this application.

U.S. Pat. No. 9,242,882 is not used in the treatment system process andonly relates to handling the smaller waste activated sludge stream withwasting of lighter solids from the waste sludge. It does not address theability to provide process conditions that favor the growth of granularbiomass over flocculent biomass. Lack of or poor growth conditions forgranular sludge will limit the ability to sustain granular sludge andthe reactor mixed liquor solids concentration attainable.

U.S. Pat. No. 9,758,405 relates to a parallel operation of aconventional flocculent activated sludge process and a SBR granularactivated sludge process with influent flow split to the two processes.The flocculent activated sludge process handles hydraulic variations ininfluent flow, while the parallel granular sludge SBR is operated withcontrolled batch feed in the same way as described in U.S. Pat. No.7,273,553 for production of PAO-containing granules. In this way thepractical problem of variations in influent flow rates are handled bythe existing flocculent activated sludge process by having continuousflow gravity separation final clarifiers for separation of treatedeffluent and return of thickened activated sludge to the process. Theparallel granular sludge SBR system provides additional wastewatertreatment capacity and is also intended to increase the biomassconcentration and capacity of the parallel flocculent activated sludgesystem by wasting excess granular sludge produced to the flocculentactivated sludge system. The average particle size of the granularsludge wasted to the flocculent activated sludge system is stated in thepatent to be less than the average size of the granules in the SBRsystem but greater than the activated sludge floc in the flocculentactivated sludge system.

U.S. Pat. No. 9,758,405 does not provide a means for assuring the growthand retention of the PAO granular sludge added from the sidestream batchreactor to the parallel activated sludge reactor. There is notnecessarily an influent wastewater/activated sludge contact zone forgrowth of PAO granules or other type of zones to favor substrate uptakeby granules over flocculent biomass. In addition, the solids retentiontime of the granules added to the continuous flow flocculent activatedsludge process would be the same as for the flocculent sludge. Thus, itonly provides a marginal benefit in the performance of the parallelactivated sludge process.

SUMMARY OF THE INVENTION

A method is provided for a continuous flow combined granular andflocculent activated sludge wastewater treatment process to removeorganics, particulates, nitrogen, and phosphorus to low effluentconcentrations with a smaller footprint than the traditional flocculentactivated sludge process. The process selects for granule biomasscapable of phosphorus and nitrogen removal and controls the average sizeof the granular sludge and the granular and flocculent sludgeconcentrations and solids retention times (SRTs).

The method comprises feeding influent wastewater to the first reactor ofan anaerobic process zone at a soluble BOD volumetric loading rate ofequal to or greater than 0.20 g soluble bCOD per liter per day, whichalso receives recycle of granular sludge from a granular sludgeclassifier with the continuous flow treatment system. The anaerobicprocess is followed by an aerobic process and then mixed liquor flowfrom the aerobic process flows through a granular sludge classifier at adesired hydraulic loading to control the granule separation from theflocculent sludge at the desired granular size. Flocculent sludge andsmaller granules are contained in the flow from the classifier to thesecondary clarifier. The flocculent sludge and other particulatessettled to the bottom of the secondary clarifier and the clarifiereffluent flow has a low TSS concentration, which enables the system tomeet effluent treatment needs. Flow from the bottom of the classifiercontaining mainly granular sludge is recycled to the first mixed reactorof the anaerobic process zone. The underflow of the secondary clarifierwhich contains mostly flocculent sludge and a much lesser amount ofgranular sludge is recycled to the aerobic process zone. Some portion ofthe secondary clarifier underflow is wasted from the system to controlthe solids retention time (SRT) and concentration of flocculent sludgein the aerobic process zone. Some portion of the classifier underflowcan also be removed to wasting for control of the system granular sludgeconcentration and SRT. The first reactor in the anaerobic process zonemay be followed by one or more additional anaerobic reactors in series.The aerobic process may consist of one or more aerated mixed reactors inseries. DO control is used to set a DO target concentration in at leastthe first aerobic zone reactor for simultaneous nitrification anddenitrification and phosphorus uptake by the granule biomass. The DOconcentration setting allows the outside layers of granules to beaerobic with nitrification and a large enough anoxic inner granulevolume to allow for denitrification by the PAOs. Control of the flowrate and liquid velocity in the classifier within a desired range forgranule size selection is enabled by a bypass flow from the aerobicprocess zone around the classifier to the secondary clarifier in thecase of high influent flow. In the case of low influent flow the flowrate to the classifier remains at the desired level by recycle flow ofthe classifier effluent to the classifier inlet and/or by recycle flowfrom the secondary clarifier underflow return sludge line.

The method may be a modification of the method described above by havingan anoxic process zone between the anaerobic process zones and theaerobic process zone. The first reactor in the anoxic process zonereceives flow from the last reactor in the anaerobic process zone andmixed liquor recycle flow from the aerobic process zone, which containsNO₃/NO₂. The anoxic process zone may consist of one or more mixedreactors in series.

The method may consist of an anoxic and aerobic process configuration toprovide nitrogen removal without EBPR. This method involves feedinginfluent wastewater at a volumetric loading rate equal to or greaterthan 0.20 g soluble biodegradable COD per liter per day to a first mixedreactor in an anoxic process zone, with the anoxic process zone followedby an aerobic process and then mixed liquor flow from the aerobicprocess through a granular sludge classifier at an desired upflowvelocity to control the desired granular size. The classifier effluentflows to a gravity secondary clarifier for effluent clarification andsettled solids removal. Flow from the bottom of the classifiercontaining mainly granular sludge is recycled to the first reactor ofthe anoxic process some. The underflow of the secondary clarifier whichcontains mostly flocculent sludge and a much lesser amount of granularsludge is recycled to the aerobic process zone. Some portion of thesecondary clarifier underflow is wasted from the system to control theflocculent sludge concentration in the aerobic process zone. Someportion of the classifier underflow can also be removed to wasting tocontrol the granular biomass concentration and SRT in the anaerobic andaerobic process zones. The first reactor in the anoxic process zone maybe followed by one or more additional anoxic reactors in series. Theaerobic process may consist of one or more aerated mixed reactors withDO control in at least the first reactor to allow for simultaneousnitrification and denitrification. The flow rate to the classifier isalso controlled in the same way as above to enable the selection ofgranular sludge within a desired size range.

The methods may comprise having two or more anaerobic reactors in seriesin the anaerobic process zone that are operated with the ability to turnoff mixers over long time intervals to allow granules and solids tosettle into a bottom sludge layer for fermentation to generate VFAs athigh concentration for consumption by PAOs. The mixers would be turnedon for a few minutes after off periods of 12 hours or more of to releasethe solids for movement to the next tank. This anaerobic reactor mayalso receive a portion of the secondary clarifier recycle sludge flow toprovide additional organic material for fermentation. The localized highVFA concentration around the settled granular sludge provides a higherbulk liquid soluble bCOD concentration to drive substrate at sufficientdepth to generate larger granular size.

The methods may include adding an exogenous source of soluble bCOD tosupport sufficient PAO growth or denitrification rates. For system lowin feed soluble bCOD external sources of VFA or other bCOD may be addedor process operation can be modified to produce VFAs. Common sourceswould be from a side reactor fermentation of waste primary sludge orpurchase of industrial carbon such as glycerol, ethanol and acetate.

The methods may include having two or more anoxic reactors in serieswith a high soluble bCOD load to the first anoxic reactor receiving theclassifier granule recycle stream and the influent wastewater.

The methods may include upflow or downflow granular sludge classifierdesigns that are located between the bioprocess and secondary clarifier.

The methods may include upflow or downflow granular sludge classifierdesigns that are located in the final tank of the bioprocess.

The methods may include upflow or downflow granular sludge classifierdesigns that are located in the secondary clarifier.

The methods may include a radial flow energy dissipator and flowdistributor apparatus located in a granular sludge classifier.

The methods may include a downflow energy dissipator and flowdistributor apparatus locate in a granular sludge classifier.

The methods may include designs for the energy dissipator that disruptthe granule/floc sludge matrix to free granules and floc.

The granular sludge must be of sufficient size to meet a high SNDefficiency so that the outer aerobic fraction of the granule is not alarge fraction of the granule biomass and the inner anoxic zone is largeenough for the necessary anoxic PAO population and bioreactions. Thesize of the granular sludge also affects the sludge settling andthickening properties. As the granular size becomes larger the granularsludge settles faster and thickens better and is more capable of SND.However, if the size is too large the biomass is used less efficientlyfor ammonia and nitrogen removal. Larger granules have less surface areaper mass and thus less area for growth of nitrifying bacteria growth. Iftoo large there is a lower nitrification and nitrogen removalefficiency. A proper size range provides both good granule sludgeseparation and selection and good nitrification and nitrogen removalefficiency.

Results reported for a SBR pilot plant provided information on factorsthat affect the granular size and SND efficiency. The reactor was 8 fthigh, 1 ft diameter and treated a stream rich in NH₃—N with acetateaddition for PAO growth. It was operated with a 1-hour anaerobic contacttime with acetate addition, 4.5 hour aerobic condition at a DO of about2.0 mg/L and short settling and decant times. Change in settling timeprovided information on the needed settling velocity of the granules toremain in the system and the size of granules obtained for thesesettling velocities. As shown in FIG. 2, granule sizes above 0.80 mmwere sufficient to have a settling velocity of 11.2 m/h. This is muchhigher than the typical settling velocity of 0.5-1.0 m/h for flocculentsludge.

As the acetate feed loading was increased the average granule sizeincreased and the SND efficiency increased to 85-99% for nitrogenremoval. At a soluble bCOD loading above 0.3-0.4 g/L-h, the granule sizeincreased to a range of 0.95 to 1.1 mm. At higher soluble bCOD loadingsthe bulk liquid soluble bCOD concentration is higher and soluble bCODdiffuses deeper into the granular depth for PAO assimilation and growthto thus produce larger size granules. Thus, a high loading is needed tofavor granule growth at 1.0 mm size and greater.

Results showed that the 1.0-1.2 mm size range provided sufficientsurface area for nitrification at a reactor loading of >0.40 g NH₃—N/L-dand high granular sludge settling velocity. The effect of the organicloading and settling velocity for granule selection is an importantfeature of the activated sludge process configuration and classifieroperation.

A prototype pilot upflow hydraulic classifier was tested for theseparation of a granular/floc sludge mixture. The activated sludge andgranules were grown on two different wastewater sources and reactors ata municipal wastewater treatment plant. The amount of granules availableallowed a test feed concentration of 1300 mg/L as granular sludge andgranule 800 mg/L for the flocculent sludge. The SVI₃₀ of the granule andflocculent sludge were 35 and 210 mL/g, respectively. The averagegranule size was 1.1 mm.

The classifier operating conditions provided an upflow velocity of 10.8m/h. The classifier underflow contained 94% of the granules fed for a 6%rejection to the stream and 36% of floc for a 64% rejection to thestream. Such a stream in the continuous flow process described in thisdisclosure would go to a secondary clarifier.

A mass balance analyses was done to determine the relativeconcentrations and SRTs of granules and flocculent sludge in thebioprocess as a function of the granular sludge classifier performanceand all solids wasting from the secondary clarifier underflow. The massbalance is based on three key fundamentals found in the wastewaterengineering textbook by Tchobanoglous et al. (2014): 1) the solidsconcentration in a bioprocess is equal to the solids production ratetimes the solids SRT divided by the bioprocess volume, 2) at steadystate operation the solids production rate is equal to the solidswasting rate, and 3) the SRT of the solids is equal to the solids massin the bioprocess divided by the amount of solids wasted per day. Thismass balance was done separately for granular and flocculent sludge. Therelative amounts of each wasted is proportional to their relativeconcentrations leaving the granular sludge classifier. For example, ifthe effluent from the classifier contains 90% of the flocculent sludgeand 10% of the granular sludge fed to the classifier, then thebioprocess will have the reverse concentrations of 90% granular sludgeand 10% flocculent sludge. Results of this mass balance are shown inFIG. 3, which shows a graph of the granular to floc SRT ratio as afunction of the classifier reject percentages.

The graph results in FIG. 3. are used to assess the efficiency of theclassifier test result and show very acceptable and good performance theupflow classifier design and operation. At a 10% granular sludge rejectand 65% reject for flocculent sludge, the system SRT for the granules is6.5 times that of the flocculent sludge. Thus, if the flocculent sludgeMLSS concentration is 1,200 mg/L for good clarification the granularsludge MLSS concentration could be as high as 7,800 mg/L. The combinedflocculent/granular sludge concentration could then be 9,000 mg/L, whichis about 3 times higher than used for conventional activated sludgeprocesses for biological nutrient removal. Higher reject efficiencieslead to higher granular mixed liquor to floc mixed liquorconcentrations.

DESCRIPTION OF THE DRAWINGS

FIG. 1 shows stereo microscope photos comparing flocculent andself-aggregating aerobic granular sludge size and structure.

FIG. 2 is a graph showing relationship of granular size, settlingvelocity and bCOD loading rate.

FIG. 3 is a graph showing relationship of a system granular to floc SRTratio as function of floc and granular sludge reject efficiency from ahydraulic separator of the feed.

FIG. 4 shows schematic of general arrangement of continuous flowcombined granular/floc sludge process.

FIG. 5A shows schematic of a variation of the process for a phosphorusand nitrogen removal including simultaneousnitrification-denitrification.

FIG. 5B shows schematic of a variation of the process for a phosphorusand nitrogen removal including simultaneousnitrification-denitrification for treating wastewater with a lowersoluble bCOD fraction.

FIG. 5C shows schematic of a variation of the process for nitrogenremoval with anaerobic granule selector zone.

FIG. 5D shows schematic of a process for production of granular sludgein sidestream treatment for feeding granules to the main wastewatertreatment process.

FIG. 6A shows schematic of a downflow granular sludge classifier.

FIG. 6B shows schematic of a upflow granular sludge classifier.

FIG. 7 shows schematic for locating the granular sludge classifier inthe bioprocess.

FIG. 8A shows schematic of a downflow granular sludge classifier locatedin the secondary clarifier.

FIG. 8B shows schematic of a submerged upflow granular sludge classifierlocated in the secondary clarifier.

FIG. 9 shows schematic of a variation of the process for nitrogenremoval with anoxic granule selector zone.

FIGS. 10A-10D show schematics of a radial flow energy dissipating inletwith radial flow for use in a granular sludge classifier.

FIGS. 11A-11B shows schematics of an energy dissipating inlet for agranular sludge classifier utilizing a downflow separation design.

DESCRIPTION OF PREFERRED EMBODIMENTS

All of the combined granular/flocculent sludge processes shown are forcontinuous flow activated sludge treatment using hydraulic granularsludge classifier to control granule size and to provide granule recycleto a first high loaded anaerobic or anoxic reactor. By continuous ismeant essentially continuous, possibly including starts and stops butnot batch process. The classifier provides a means to control the sizeof the granular sludge and the flocculent and granular sludgeconcentrations in the treatment reactor activated sludge mixed liquor. Aminimum flocculent sludge concentration is needed for efficientdegradation of colloidal and suspended solids in the wastewater and toprovide good effluent clarity.

The flocculent sludge concentration may vary as a function of thewastewater characteristics and will be typically in the range of500-1,500 mg/L. A preferred range of flocculent sludge for solidsclarification for capture of particulates and colloidal solids is 800mg/L-1,200 mg/L. The granular size is controlled to provide a low SVIand a high MLSS concentration and for maintaining high efficiencysimultaneous nitrification-denitrification (SND) and enhanced biologicalphosphorus removal (EBPR). The size must be large enough to provide asufficient anoxic volume in the granules in the aerobic reactor for SNDand PAO growth, but small enough to provide efficient use of biomassgrowth for EBPR and have enough surface area for efficientnitrification. The granules may have a size range from 0.3 mm-3.0 mm.The preferred size may be in the range of 0.7 mm-2.0 mm. The effluentfrom the classifier has a much higher concentration of flocculent sludgethan granular sludge and these solids are settled in the secondaryclarifier. The secondary clarifier can be circular, rectangular orsquare. Wasting of sludge from the bottom flow from the secondaryclarifier results wasting more flocculent than granular sludge from thesystem to thus result in a much higher granule sludge concentration inthe bioprocess. Concentrations and SRTs in the reactor mixed liquor. Thegranular sludge concentration in the mixed liquor may be 2-8 times theflocculent sludge concentration, or in the first process zone, typically2-3 times. Due to the high settling rates and high thickness of thegranular sludge the bioprocess may have a reactor mixed liquorconcentration 2-3 times that of conventional flocculent activated sludgesystems and up to a typical operating range of 6,000 mg/l-12,000 mg/L tosave on treatment footprint and tank volume required. The hydraulicseparator provides an upflow velocity that carries out mostly flocculentsolids to be removed by the final clarification step.

Granule settling velocity changes with granule size and thus thehydraulics of the classifier are controlled to select for the desirablegranular size. Other types of classifiers may be used in thecombined/flocculent sludge processes for granule size selection and flocseparation such as screens or hydrocyclones.

FIG. 4 shows a general arrangement of the process for granule selectionand granule size and concentration control. Granular sludge recycle flowline 21 enters an anaerobic or anoxic reactor 36 at high soluble bCODloading where it is mixed with the influent wastewater line 16. Flowfrom the high loaded reactor is further processed in a downstreamaerobic or anoxic reactors and in aerobic reactors consisting of one ormore baffled stages. The flow from the final aerobic process line 28enters the classifier 10 which produces two outflow streams. One flowcontains mostly flocculent sludge line 22 which is directed to thesecondary clarifier. The other flow contains mostly granules which isdirected to the first reactor via line 21 with possible removal of asmall portion line 26 for granular sludge wasting.

Flow control methods are used to maintain the hydraulic loading on theclassifier with possible upflow velocities in the range of 5-20 m/h(meters per hour) to control granule size selection and maximize theflocculent sludge rejection efficiency. Rejection represents thefraction of granule or floc solids from the influent line 28 that is inthe classifier effluent line 22. A high rejection percentage occurs forthe smaller size flocculent sludge and a lower rejection percentageoccurs for the larger size faster settling granules. A portion of theflow leaving bioprocess may be bypassed around the classifier in abypass line 30 to divert higher flows during diurnal flow variations ordue to wet weather events to control the flow rate to the classifier.When the influent wastewater flow results in lower than a desired rangeof flow to the classifier, recycle may be provided from the classifiereffluent line 32 and/or by increasing the flow of clarifier returnsludge line 18. Short cut recycle from line 18 can be used to directrecycle sludge flow to the classifier via line 19.

Sludge wasting must be done to control the activated sludge MLSSconcentration at its desired levels. The primary location for wastingexcess solids is line 34 from the secondary clarifier. The classifierprovides a higher percentage of flocculent sludge to the clarifier dueto the higher reject efficiency for the smaller solids. Thus, thesecondary clarifier underflow has a higher fraction of flocculent sludgeand wasting from that line results in a bioprocess with a much highergranular sludge concentration than flocculent sludge.

The sludge management approach is also to select the solids wasting ratefrom the secondary clarifier underflow line 34 to meet the flocculentsludge concentration needed to provide good clarification and low TSS inthe effluent. If the SRT and bioprocess concentration of the granularsludge is too high than additional granular sludge can be wasted fromthe classifier underflow line 26.

The embodiments illustrated in FIGS. 5A, 5B, 5C, FIG. 5D, and FIG. 9 arefor continuous flow combined granular/flocculent activated processeswith different process features to meet the specific treatmentobjectives, handle different types of wastewater characteristics andselect for the preferred type of granular sludge. They all incorporate ahigh loaded first reactor and granular sludge classifier to control thegranular sludge size and relative proportions of granular and flocculentsludge in the activated sludge mixed liquor. Granule size control isimportant for providing an aerobic reactor with SND, which reducesenergy costs for aeration and internal recycle pumping and a simplertreatment scheme than conventional nitrification and denitrificationprocesses for nitrogen removal.

The first embodiment shown in FIG. 5A is a continuous flow combinedgranule/flocculent sludge process to grow granules with PAOs and toallow SND to achieve for both biological nitrogen and phosphorusremoval. The process has an anaerobic zone 38, an aerobic zone with SND40, a final aerobic zone at higher DO 52, granular sludge classifier 10,and a secondary clarifier 14.

Granular sludge is recycled from the classifier line 21 to an anaerobicreactor 42 with a volume that result in a high soluble bCOD loading fromthe influent flow line 16. The anaerobic zone may have at least 3 stages(3 mixed reactors in series) with the first reactor at a high solublebCOD loading of greater than 4.8 g soluble bCOD/L-day and less than 30 gsoluble bCOD/L-day. The 2^(nd) stage volume 44 is at least as large asthe 1^(st) stage and preferably no more than double. The 3^(rd) stage 46is much larger and can exist as a single tank or be divided intomultiple stages. The high soluble bCOD loading assures a higher bulkliquid soluble bCOD concentration and creates a long enough diffusiongradient to drive substrate deeper into the granules for subsequentoxidation by NO₃/NO₂ for SND in the aerobic zone to enable larger sizegranules.

Mixed liquor from the anaerobic zone enters 38 enters an aerobic reactor40 that has DO control to allow SND. If DO concentration is too highthen oxygen penetrates too deep into the granule to limit use of NO₃/NO₂by the PAOs. If too low the nitrification rate on the outer layer of thegranules is too low to result in a low nitrification efficiency. A lowernitrification efficiency can lead to less nitrogen removal.

The aeration tank 40 can be a single aerated mixed tank or divided intoa number of tanks in series. Aeration DO control maintains the DOconcentration at set points in the range of 0.5 mg/L-2.5 mg/L dependingon the MLSS and granular size so that SND occurs for nitrogen removal.Nitrifying bacteria growth is primarily on the outer layers of thegranule, where the DO concentration is higher, and PAOs are generally inthe inner core of the granule, which can use NO₃/NO₂ produced bynitrifying bacteria in the outer granule.

The classifier and secondary clarifier process and operation is the sameas that described for FIG. 4 above. One exception is that the increasedreturn activated sludge recycle flow to control the classifier velocitymay also be provided in a separate flow line 19 from the returnflocculent sludge recycle instead of only increasing the flow in line18.

The sludge wasting to control the bioprocess granular and flocculentsludge concentrations is the same as described for the generalconfiguration in FIG. 4 above.

Anaerobic zone stages after the 1^(st) stage 42 may be operated withon/off mixing to allowed solids settling and fermentation of solids toproduce more localized soluble bCOD for uptake by granules with PAOs.Some return activated sludge flow line 18 a may be added to theanaerobic stage with on-off mixing to provide other solids that can befermented to produce soluble bCOD.

A modification to Embodiment 1 for wastewater with a low influentsoluble bCOD relative to the influent total organic and ammonia nitrogenis shown in FIG. 5B. The modification relies on the degradation ofparticulate and colloidal solids to provide degradable COD fordenitrification. This process contains an anaerobic zone 38 anoxic zone50, a SND aerobic zone 40, a second aerobic zone 52, a low DO zone 54, agranular sludge classifier 10, and a secondary clarifier 14.

This process is necessary for applications lacking enough soluble bCODto enable high removal of nitrogen by SND with PAO granular sludge. Dueto the low soluble bCOD:N ratio the amount of stored carbon by PAOs inthe anaerobic zone cannot provide enough electron donor to consume ahigh percentage of the amount of NO₃/NO₂ produced in the aerobic zone.An internal recycle flow, line 56, from the low DO zone 54 within thesecond aerobic zone 52 provides NO₃/NO₂ to the unaerated mixed anoxiczone 50 for consumption of NO₃/NO₂ with oxidation of particulate andcolloidal solids. The internal recycle flowrate may range from 50 to500% of the wastewater influent flowrate. The anoxic and aeration zonesmay consist of a single reactor or a number of reactors operated inseries.

Additional carbon is provided by biodegradable colloidal and suspendedsolids in the preanoxic zone 50 before the aerobic SND zone 40. Theadditional aerobic zone 52 operated at a higher DO concentration isprovided after the SND aerobic zone for further NH₃ oxidation andenhance further P uptake.

For this process all the features and operational conditions of theanaerobic zone 38, SND aerobic zone 40, final aerobic zone 52 describedfor FIG. 5A are applicable. Also, all the features and operationalconditions described for the classifier and clarifier and sludgemanagement are applicable and clarifier operation described inEmbodiment 1 above with FIG. 5A are included.

A modification to Embodiment 1 for applications for which nitrogenremoval and not phosphorus is required is shown in FIG. 5C. An anaerobichigh loaded first reactor is used to select for PAO granules. Mixedliquor flows from anaerobic reactor 44 to an anoxic zone 50 that may besingle or multiple stages. The PAO granules from reactor 44 use storedcarbon obtain in reactors 42 and 44 for denitrification in zone 50.

Embodiment 2 shown in FIG. 5D is used for growth of granules to add tothe main treatment system and does not have a final secondary clarifieras in Embodiment 1. The first high loaded anaerobic reactor 42 is fedline 16 a which may be a reject liquid from digestion dewatering or asmall portion of the influent wastewater flow. The process selects forPAO granules that are fed via line 26 a to a liquid treatment systemproducing the treated effluent for the wastewater treatment plant. Theclassifier overflow final effluent line 23 a is also fed to the mainliquid treatment system. Treatment of influent flow 16 a follows thesame course as for the system in FIG. 5A to produce PAO granules.Recycle of underflow from the classifier 10 is directed to reactor 42operated at a high soluble bCOD load. This sidestream granulargenerating system may be fed anaerobic digestions dewatering rejectwater supplemented with organic carbon, part of the wastewater plantinfluent stream or other.

The sludge classifier is the key component for the control andoptimization of granular/flocculent activated sludge processes.

The sludge classifier uses a hydraulic design to control the relativecapture efficiency of granules and floc and to also control the size ofthe granular sludge. The classifier is a downflow or upward feed andupflow effluent design that separates the appropriate solids size as afunction of the apparatus upflow velocity. The upflow velocity isgreater than 1.0 m/hr to minimize floc settling in the lower chamber.The classifier may be contained in the bioreactor tankage as shown inFIG. 7, located between the bioreactor and liquid/solids separationclarifier as shown in FIGS. 6A and 6B, or located within a conventionalsecondary clarifier as shown in FIGS. 8A and 8B.

A schematic of the granular/flocculent downflow classifier 10 a locatedbetween the bioreactor and liquid/solids separation clarifier is shownin FIG. 6A. The effluent flow line 28, from the aerobic process zoneplus classifier effluent recycle flow line 32, enters an energydissipater 60, preferably but not necessarily submerged, thatdistributes a uniform down flow of the mixed liquor and promotesseparation of granule and floc. The flow travels downward in the innerchamber 62 and the fast settling granules continue to settle to thebottom of the classifier. A majority of the flow from the inner chamberflows to the outer chamber 63 and the resulting liquid rise velocity inthe outer chamber is greater than the floc settling velocity of floc,which causes floc to be carried upward and out with the flow over theeffluent launder 64 to the secondary clarifier through the classifiereffluent line 22. Due to the fact, granular sludge has a much highersettling velocity than flocculent sludge, the solids rising in the outerchamber will consist mainly of flocculent sludge. The rise rate can alsobe controlled to select for granular size by varying the recycle flowrate line 32. At very high flow rates, due to peak diurnal flow or wetweather flow, a portion of the influent flow to the classifier can bebypassed using the high flow bypass line 30 to the secondary clarifierso that the classifier's preferred rise rate is maintained. The granulesare collected and thickened at the bottom of the classifier 10 a andexits via line 20 to continuous flow recycle line to the high loadgranular biomass selector tank at the beginning of the upstreamactivated sludge process and also split to a waste line to be used asneeded.

A schematic of the granular/flocculent sludge upflow classifier 10 blocated between the bioreactor and liquid/solids separation clarifier isshown in FIG. 6B. The influent feed from the activated sludge bioreactorline 28 plus the effluent recycle flow line 32 is introduced into theenergy dissipater 68 preferably submerged and located at an appropriatedepth within the classifier that distributes a uniform radial flow andpromotes separation of granules and floc. Preferably the dissipater isbetween one-third and two thirds of the classifier tank liquid depth, orwithin 30% of center of the tank's depth. The classifier's dimension andtotal feed flow rate determine the upflow velocity in the upper regionof the chamber 66 to separate granules and floc and determine thegranule size. The granules with settling velocity greater than theupflow velocity are captured and thickened at the bottom of theclassifier 10 b and exits via line 20 to a continuous flow recycle lineto the high load granular biomass selector tank at the beginning of theupstream activated sludge process and also split to a waste line to beused as needed. The rise rate can also be controlled to select forgranular size by varying the recycle flow rate, line 32. At very highflow rates due to peak diurnal flow or wet weather flow a portion of theinfluent flow to the classifier can be bypassed using the peak flowbypass line 30 to the secondary clarifier so that the classifier desiredrise rate is maintained.

In a preferred embodiment of the system of the invention the classifierprocesses at least two times daily system influent volume per day.

The general schematic in FIG. 7 illustrates that the classifier can belocated in the bioprocess, typically after the last aeration reactor.Granular sludge recycle flow from the classifier line 21 enters agranular feed reactor 36 at a high soluble bCOD loading where it ismixed with the influent wastewater line 16. The granular feed reactor 36may be anaerobic (as in FIGS. 5A, 5B, and 5C) or anoxic (as in FIG. 9).The bioprocess zone 48 after the granular feed reactor may contain aseries of anaerobic, anoxic and aerobic reactors in some configuration.Mixed liquor flow from a final bioprocess reactor enters the classifier10 and most or all of the flow in the classifier underflow line is inthe granular sludge recycle line 21 or a lesser amount for granularsludge wasting line 26. Flow control to the classifier at low influentflow conditions may be provided by recycle of flow from the classifiereffluent line 22 back to the classifier inflow via line 32 and/or byincreasing the flocculent sludge recycle flow rate from the secondaryclarifier 14 via line 18. At excessive high flow conditions bioprocesseffluent flow beyond that desired for the classifier may be directedfrom the final bioprocess reactor to the clarifier 14 via line 30. Thetotal influent flow line 23 to the clarifier 14 equals the clarifiereffluent flow following solids settling line 24 plus clarifier underflowwith a thicker flocculent sludge concentration in a recycle flow to thebioprocess 48 and a small amount of flow for mainly flocculent sludgewasting line 34.

A schematic of the granular/flocculent downflow classifier locatedwithin a conventional secondary clarifier is shown in FIG. 8A. Theeffluent flow line 28 from the activated sludge bioreactor plusclarifier floc recycle flow line 19 enters an energy dissipater 70 thatdistributes a uniform down flow of the mixed liquor and promotesseparation of granules and floc. Alternatively, the recycle flow rate tothe bioprocess in line 18 could be increased. The flow travels downwardin the inner, classifier chamber 72, the granules are settling fasterthan the floc. Floc from the classifier chamber 72 flows into the outer,secondary clarifier chamber 74 with an upflow velocity that liftsparticles with settling velocity less than the rise velocity. Flow istoward the effluent launder 76. Floc then is allowed to settle to thebottom of the secondary clarifier chamber 74 and the clarifier liquid iscarried into the effluent launder and out through the clarified effluentline 96. Due to the fact that granular sludge has a much higher settlingvelocity than flocculent sludge, the solids leaving the classifierchamber 72, i.e. flowing outwardly between an upper annular deflector 80and a lower annular sludge dividing deflector 82 will consist mainly offlocculent sludge. The rise rate in the classifier chamber 72 can alsobe controlled to select for granular size by varying the clarifier flocrecycle flowrate line 32. At very high flow rates due to peak diurnalflow or wet weather flow a portion of the influent flow to theclassifier can be bypassed using the high flow bypass line 30 to aseparate secondary clarifier so that the classifier preferred rise rateis maintained. The granules are collected and thickened at the bottom 78of the classifier chamber 72 and recycled, via line 84, to the highloaded first reactor of the upstream activated sludge process. The flocare also collected and thickened at the bottom of the secondaryclarifier chamber 74 and recycled, via line 86, to the appropriatelocation in the upstream activated sludge process.

A schematic of a more preferred embodiment of a granular/flocculentupflow classifier located within a conventional secondary clarifier isshown in FIG. 8B. The effluent flow from the activated sludgebioreactor, line 28, plus clarifier floc recycle flow line 19 enters anenergy dissipater, flow distribution, and granule/floc separation device88 located at an appropriate depth within the inner, classifier chamber92, preferably below center as shown. This combined influent flow entersthe separation device 88 via ports (not shown) in the center influent 90of the clarifier. The flow travels upward and outward, the granules aresettling faster than the floc and tend to settle in the classifierchamber 92 of the clarifier. Floc from the classifier chamber 92 flowsinto the outer, secondary clarifier chamber 94 with an outward andupward flow velocity that lifts particles with settling velocity lessthan the rise velocity. Again, upper and lower annular deflector plates80 and 82, respectively, help direct flow in and out of the classifierchamber 92. Floc flows out of the classifier chamber to the secondaryclarifier chamber 94. Floc is allowed to settle to the secondaryclarifier floor in the secondary clarifier chamber and the clarifiedliquid is carried into the effluent launder 76 and out through theclarified effluent line 96. Due to the fact that granular sludge has amuch higher settling velocity than flocculent sludge, the solids leavingclassifier chamber 92 will consist mainly of flocculent sludge. The riserate in the classifier chamber 92 can also be controlled to select forgranular size by varying the clarifier floc recycle flowrate line 19. Atvery high flow rates, due to peak diurnal flow or wet weather flow, aportion of the influent flow 28 to the classifier can be bypassed usinga high flow bypass line 30 to a separate secondary clarifier so that theclassifier preferred rise rate is maintained. The granules are collectedand thickened at the bottom of the classifier chamber 92 and recycledline 84 to high loaded first reactor of the upstream activated sludgeprocess. The floc are also collected and thickened at the bottom of thesecondary clarifier chamber 94 and recycled, via line 86, to theappropriate location in the upstream activated sludge process.

Embodiment 3 shown in FIG. 9 is for a continuous flow combinedgranular/flocculent sludge process for nitrogen removal where phosphorusremoval is not needed. No anaerobic zone is used in this case and thegranules grown are based on the classifier operation and the solublebCOD loading to the first stage reactor 54 of the anoxic zone 50. Theprocess contains an anoxic zone 50, an aerobic zone 40, a granularsludge classifier 10 and secondary clarifier 14. The second anoxicreactor 58 may be single stage or divided into two or more stages. Theaerobic zone 40 may also be single stage or divided into two or morestages.

All the features and operational conditions described for the classifierand clarifier and sludge management are applicable and clarifieroperation described in Embodiment 1 above with FIG. 5A are included.

FIGS. 10A through 10D show an energy dissipating inlet (EDI) 110 thatcan be used in the preferred classifier shown in FIG. 6B. This issometimes called a reverse energy dissipating inlet or reverse EDI, andcan be used upright as in FIGS. 10A and 10B, or inverted as in FIGS. 10Cand 10D. The EDI has a top plate 112, a top deflector plate 114 at theperiphery of the top plate, a bottom plate 116 and a series of outer andinner baffle plates 118 and 120, offset in position as shown in FIG.10D, which shows a preferred inverted condition of the EDI 110. Thesectional view of FIG. 10D is also inverted, showing inner baffles at120 and the outer baffles 118 in dashed lines, since they are instaggered positions with the inner baffles at baffle. In this positionthe top plate 112 is actually at the bottom. As can be seen from FIGS.10C and 10D, flow is down through the influent pipe 122 to the interiorof the EDI, where the baffles dissipate energy, slow and distribute theflow generally evenly into the volume of liquid, tending to separate thefloc and granular sludge, with an upward and outward flow pattern.

FIGS. 11A and 11B show an energy dissipating inlet (EDI) 121 that can beused in the classifier shown in FIG. 6A and in the classifier area ofthe clarifier in FIG. 8A utilizing the downflow separation design. Thisis sometimes called a faucet energy dissipating inlet, and can be usedwith faucet baffles at bottom of the lower deflector 124 as in FIG. 11A,or at the bottom plate 116 as in FIG. 11B. The EDI 121 has a bottomplate and a series of outer and inner baffles (118 and 120) similar tothe reverse EDI 110 shown in FIGS. 10A through 10D. EDI 121 also hasmore baffled layers 119 than EDI 110 with each baffled layer, from themost inner to the most outer, offset from each other to provideincreased energy dissipation and optimum flow patterns to disrupt thegranule/floc matrix for optimum separation of granules from the flocstructure. In addition, upper faucet baffling system in FIG. 11A or alower faucet baffling system in FIG. 11B is added to equalize flowdistribution of the granules which have separated from the flocstructure such that the granules settle over the entire classifier floorarea. The faucet baffle system has openings which vary in size so thatthe beginning flow is restricted from exiting the closest opening andrequires the flow to continue flowing to the next opening until the flowis equalized. The faucet layer can be placed at the lower exit of theEDI 121 which is referred to the lower faucet baffles 126 as shown inFIG. 11A, or this faucet baffle system can replace a portion of thebottom plate 116 at the upper exit which is referred to the upper faucetbaffles 128 shown in FIG. 11B. The lower faucet baffles 126 in FIG. 11Areceive the settled granules from the upper layer of radial baffles atthe outer edge of the bottom plate 116. The lower faucet baffles 126, inthis configuration, restrict all the granules from exiting at the outeredge of the lower deflector 124 requiring the flow to continue flowingto the next opening until the flow is equalized and the granules settleevenly over the entire classifier floor area. In contrast, the upperfaucet baffles 128 in FIG. 11B allow the granules that have settled ateach radial baffle layer to pass through the faucet opening while thefloc is kept suspended, enters an outer annular part, still high up inthe EDI as shown, and finally exits through an annular array of flocdischarge outlets 131 along an upper deflector 130 which directs thefloc 132 outwardly and downwardly into the clarifier area. After passingthrough the upper faucet baffles 128, the granules 134 then settleevenly over the entire classifier floor area of the tank with the lowerdeflector 124 preventing short circuiting into the clarifier area of thetank.

Terms used herein such as “about” or “generally” should be understood asmeaning within 10% of the value stated.

The above described preferred embodiments are intended to illustrate theprinciples of the invention, but not to limit its scope. Otherembodiments and variations to these preferred embodiments will beapparent to those skilled in the art and may be made without departingfrom the spirit and scope of the invention as defined in the followingclaims.

We claim:
 1. A wastewater treatment system for biological treatment ofwastewater including organic sewage, the system including a liquidprocess configuration for removal of at least nitrogen and forconcentrating biomass, in a continuous flow process, comprising: aplurality of process zones, including a first process zone receivinginfluent wastewater in continuous flow and mixing the influentwastewater with biomass to produce a mixed liquor in the first processzone, and including bacteria in the first process zone effective toproduce granular biomass as well as flocculent biomass, the firstprocess zone being anaerobic or anoxic to encourage formation ofgranular biomass, the plurality of process zones including at least asecond process zone receiving mixed liquor in continuous flow from thefirst process zone, including granular biomass and flocculent biomass,the process zones including an aerobic zone, a biomass classifierdownstream of the process zones, receiving mixed liquor with granularand flocculent biomass, the classifier having separation means forseparating out most of the granular biomass from the mixed liquor, sothat the classifier produces a first effluent with predominantlyflocculent biomass and a second effluent with predominantly granularbiomass, a gravity settling clarifier downstream of the classifier andreceiving said first effluent from the classifier, the clarifier havinga bottom where settled sludge is collected, first recycle means carryingsaid second effluent from the classifier back to the first process zone,while at least periodically wasting a portion of the second effluent,second recycle means for moving a major portion of settled sludgecollected in the clarifier bottom to the aerobic process zone, while awaste outlet of the clarifier at least periodically wastes anotherportion of the settled sludge from the clarifier, third recycle meansfor balancing variations in influent flow rate into the system wheninfluent flow is below a desired range, either by recycling a selectedportion of said first effluent from downstream of the classifier toupstream of the classifier or by increasing flow at said second recyclemeans, and a bypass line for moving a selected portion of biomass fromthe process zones in a bypass around the classifier, in an amount tobalance variations in influent flow rate to the system above the desiredrange.
 2. The wastewater treatment system of claim 1, wherein the secondrecycle means delivers a further portion of settled sludge from theclarifier bottom to an anaerobic process zone.
 3. The wastewatertreatment system of claim 1, wherein the classifier includes aclassifier waste outlet enabling at least a periodic wasting of a partof said second effluent.
 4. The wastewater treatment system of claim 1,wherein the biomass classifier includes an energy dissipating inletdirecting said mixed liquor into the classifier, the mixed liquorflowing into and through the classifier at a generally consistent flowrate, such that mostly granular biomass, having a greater density thanfloc biomass, settles and collects at the bottom of the classifier to bedischarged as said second effluent, while floc biomass exits theclassifier near an upper end of the classifier at said first effluent.5. The wastewater treatment system of claim 4, wherein the energydissipating inlet for the mixed liquor is submerged and includes bafflesto slow and distribute the flow of mixed liquor into the classifier, theenergy dissipating inlet being configured to direct inflow upwardly andoutwardly in the classifier, to promote separation of granular sludgefrom floc sludge.
 6. The wastewater treatment system of claim 4, whereinthe energy dissipating inlet for the mixed liquor is submerged andincludes baffles to slow and distribute the flow of mixed liquor intothe classifier, the energy dissipating inlet being configured to directinflow outwardly and downwardly in the classifier, the baffles promotingseparation of granular sludge from flow sludge.
 7. The wastewatertreatment system of claim 6, wherein the energy dissipating inlet isconfigured to direct incoming mixed liquor radially outwardly andevenly, horizontally in all directions with the baffles being atstaggered positions in the path of radial flow, then to direct flow froman upper, outer annular part of the EDI downwardly and through a seriesof radially spaced openings to direct a primarily granular flowdownwardly, and the outer annular part including an annular array ofoutlets for mixed liquor just downstream of the baffles, to releaseprimarily flocculent mixed liquor.
 8. The wastewater treatment system ofclaim 1, wherein the classifier has a wasting outlet connected to theclassifier bottom, so that wasting of settled sludge at both theclarifier and the classifier can be adjusted to provide desiredproportions of granular sludge and of floc sludge in the process zones.9. The wastewater treatment system of claim 1, wherein the process zonesinclude an anaerobic zone as a first zone and an aerobic zone downstreamof the anaerobic zone, and wherein primarily granular sludge from theclassifier is recycled to the anaerobic zone, while primarily flocsludge from the clarifier is recycled to the aerobic zone.
 10. Thewastewater treatment system of claim 1, wherein the process zonesinclude an anaerobic zone, an anoxic zone downstream of the anaerobiczone, and an aerobic zone downstream of the anoxic zone.
 11. Thewastewater treatment system of claim 1, wherein the process zonesinclude an anoxic zone and an aerobic zone, and wherein primarilygranular sludge from the classifier is recycled to the anoxic zone,while primarily floc sludge from the clarifier is recycled to theaerobic zone.
 12. The wastewater treatment system of claim 1, furtherincluding means for varying a flow rate of the second recycle means tobalance variations in influent flow to the system.
 13. The wastewatertreatment system of claim 1, further including means for local recyclearound the classifier in a selected amount to balance variations ininfluent flow to the system.
 14. The wastewater treatment system ofclaim 1, wherein the first process zone is receiving influent wastewaterat a soluble bCOD loading rate of at least 4.8 g/L/day.
 15. Thewastewater treatment system of claim 1, wherein the mixed liquor in thefirst process zone has a flocculent biomass concentration in the rangeof 500 to 2,000 mg/L.
 16. The wastewater treatment system of claim 1,wherein the mixed liquor in the first process zone has a granularbiomass concentration in the range of 2,000 to 12,000 mg/L.
 17. Thewastewater treatment system of claim 15, wherein the mixed liquor in thefirst process zone has a granular biomass concentration in the range ofabout 3,000 to 9,000 mg/L.
 18. The wastewater treatment system of claim1, wherein the granular biomass in the process zones is at a granulesize in the range of about 0.3 to 3.0 mm.
 19. The wastewater treatmentsystem of claim 1, wherein the granular biomass in the process zones isat a granule size in the range of about 0.7 to 2.0 mm.
 20. Thewastewater treatment system of claim 1, wherein mixed liquor flowthrough the biomass classifier is at a rate greater than 1 meter perhour.
 21. The wastewater treatment system of claim 20, wherein mixedliquor flow through the biomass classifier is at a velocity in the rangeof 5 to 20 meters per hour.
 22. The wastewater treatment system of claim1, wherein granular biomass concentration in the first process zone istwo to three times floc biomass concentration.
 23. In a biologicalwastewater treatment system, a classifier for separating granular sludgefrom flocculent sludge, comprising: a tank or vessel, having an infeedof biomass sludge to the tank including both granular and flocculentsludge, an energy dissipating inlet in the tank and receiving the infeedand dispersing it into the tank at a reduced velocity, the tank havingan effluent outflow near the top of the tank, causing a flow pattern inthe tank ultimately upwardly toward the outflow, such that the upwardflow carries primarily floc biomass of less density than granularbiomass to the outflow, while primarily granular biomass, with higherdensity than the floc biomass, settles toward the bottom of the tank toaccumulate at the bottom of the tank, and at the bottom of the tank, abottom outflow for removal or recycle of granular floc, whereby amajority of biomass at the bottom outflow of the tank is granularbiomass, and a majority of biomass effluent exiting the outflow near topof the tank is floc biomass.
 24. The system of claim 23, wherein theenergy dissipating inlet is submerged, positioned generally centrally inthe height of the tank, within 30% of the tank height from center. 25.The system of claim 23, wherein the energy dissipating inlet issubmerged deeply in the tank, approximately ⅓ to ⅔ down through thedepth of the tank, and configured to direct a current of sludgeoutwardly and upwardly from the energy dissipating outlet.
 26. Thesystem of claim 23, wherein the bottom of the tank tapers to a narrowbottom point, at the bottom outflow.
 27. The system of claim 23, whereinthe energy dissipating inlet comprises a generally circular body with atop having a sludge inlet leading to an interior of the body, a bottomdefining a lower boundary of the body, and a series of verticallyextending baffle plates extending between the bottom and top of the bodyto disperse sludge and establish a generally even distribution of sludgeentering the tank.
 28. The system of claim 23, including a recycle pathreturning effluent from the effluent outflow back to the classifierinlet, to recycle a portion of the effluent as needed to maintain adesired range of flow through the classifier even under varying diurnalflow conditions.
 29. The system of claim 28, further including a bypassfrom upstream of the infeed to downstream of the effluent outflow, tobypass a portion of the infeed as needed to maintain a desired range offlow rate through the classifier even under varying diurnal flowconditions.
 30. The system of claim 23, further including a bypass fromupstream of the infeed to downstream of the effluent outflow, to bypassa portion of the infeed as needed to maintain a desired range of flowrate through the classifier even under varying flow conditions.
 31. Thesystem of claim 23, including a wasting line connected to the bottomoutflow of the classifier tank.
 32. The system of claim 23, wherein thesubmerged energy dissipating inlet for the mixed liquor includes bafflesto slow and distribute the flow of mixed liquor into the classifier, theenergy dissipating inlet being configured to direct inflow upwardly andoutwardly in the classifier, to promote separation of granular sludgefrom floc sludge.
 33. The system of claim 23, wherein the energydissipating inlet is configured to direct incoming mixed liquor radiallyoutwardly and evenly, horizontally in all directions with the bafflesbeing at staggered positions in the path of radial flow, then to directflow from an outer annular part of the EDI downwardly and through aseries of radially spaced openings to direct a primarily granular flowdownwardly, and the outer annular part including an annular array ofoutlets for mixed liquor just downstream of the baffles, to releaseprimarily flocculent mixed liquor.
 34. A method for enhancing biologicalnitrogen and/or phosphorus removal from sanitary sewage wastewater, in acontinuous flow process, comprising: operating a biological MLSS processin one or a succession of process zones, to remove nitrogen or nitrogenand phosphorus from activated sludge, and continuously receiving new rawinfluent wastewater into the process zones, a first zone of said processzones being an anaerobic or anoxic zone, directing sludge flow from thebiological MLSS process zone(s) through a classifier through whichsludge flows and in which granular sludge is mostly separated from flocsludge, directing primarily granular sludge in a granular recycle flowfrom the classifier back to one of the biological process zones,directing primarily floc sludge out of the classifier and to a clarifierwhere sludge settles to the bottom of the clarifier, recycling a majorportion of the settled sludge from the clarifier to one of the processzones, in a classifier recycle, increasing flow into the classifiereither by returning a portion of the primarily floc sludge exiting theclassifier to an input of the classifier or by increasing the recycle ofsettled sludge from the clarifier, when the classifier recycle isoperated, with a classifier bypass line, bypassing a portion of sludgefrom the biological process around the classifier when the classifierbypass line is operated, operating the classifier recycle and theclassifier bypass line to maintain a flow rate into the classifierwithin a desired range during influent flow variations, by increasingflow through the classifier recycle when influent flow falls below thedesired range and increasing flow through the classifier bypass linewhen influent flow exceeds the desired range, operating the classifiersuch that granular sludge separated out in the classifier is in a sizerange from about 0.3 to 3.0 mm, and operating the classifier and wastingsettled sludge from the classifier and from the clarifier at such ratesas to establish a desired ratio of granular sludge to floc sludge in theprocess zones.
 35. The method of claim 34, wherein said one of theprocess zones to which the primarily granular sludge is directed to ananaerobic zone.
 36. The method of claim 34, wherein the granular sludgesize range is about 0.7 to 2.0 mm.
 37. A classifier within a clarifierin a system for biological treatment of wastewater including organicsewage, comprising: a clarifier tank with an inflow pipe receivingactivated sludge from upstream liquid process zones of the system, theclassifier including an energy dissipating inlet connected to the inflowpipe and receiving sludge having both floc and granular biomass, theenergy dissipating inlet having a top plate and a bottom plate andinternal baffles configured to direct sludge in generally opendistribution radially outwardly into liquid volume of the clarifier,such that sludge solids settle by gravity to a tank floor slopeddownwardly toward the center of the clarifier, with granular sludgesettling faster than floc sludge and the floc sludge settling slower andmore outwardly, the classifier further including the clarifier having agranular sludge exit through the tank floor, near the center of theclassifier, and a floc sludge exit through the tank floor spacedoutwardly from the granular sludge exit, the classifier furtherincluding an annular sludge dividing deflector plate extending up fromthe tank floor and positioned radially inwardly from the floc sludgeexit, so that floc sludge, which tends to settle more slowly and travelfarther outwardly in the clarifier than granular sludge, tends to settleon the tank floor outwardly of the dividing deflector plate while thedenser granular sludge tends to settle inwardly of the dividingdeflector plate, whereby sludge exiting the granular sludge exit has ahigher concentration of granular sludge than sludge exiting at the flocsludge exit of the clarifier.
 38. The classifier as in claim 37, whereinthe clarifier has a rotating sludge removal arm positioned on andmovable on the clarifier floor in a sweeping motion to bring settledgranular sludge to the granular sludge exit, and including a floc sludgeremoval arm on the clarifier floor and movable in a sweeping motion tobring floc sludge to the floc sludge exit.
 39. The classifier as inclaim 37, further including an upper deflector plate in an annularconfiguration above and outward from the energy dissipating inlet,positioned to deflect sludge emerging from the energy dissipating inletaway from a liquid surface in the clarifier and outwardly in theclarifier.
 40. (canceled)
 41. The classifier as in claim 37, wherein theenergy dissipating inlet has a downflow configuration, with internalbaffles configured to direct floc biomass in generally even distributionradially outwardly and upwardly to exit a floc discharge opening intoliquid volume of the clarifier and faucet baffles to direct granularbiomass in generally even distribution radially inwardly and downwardlyinto the liquid volume.
 42. In a wastewater treatment system, asidestream treatment process for generating granular biomass for use ina mainstream process for removing nitrogen and/or phosphorus,comprising: operating a biological sludge process in one or a successionof process zones, to remove nitrogen or nitrogen and phosphorus fromactivated sludge, and continuously receiving solids processing rejectwater or influent wastewater into the process zones, a first zone ofsaid process zones being an anaerobic or anoxic zone, directing sludgeflow from the biological sludge process zone(s) through a classifierthrough which sludge flows and in which granular sludge is mostlyseparated from floc sludge, and collecting primarily granular sludge ina bottom area of the classifier, recycling a majority of the primarilygranular sludge to the first zone so as to feed the granular biomasswith influent soluble bCOD, and wasting a sidestream comprising some ofthe primarily granular sludge to the mainstream process.
 43. The processof claim 42, wherein the classifier has a primarily floc sludgeoverflow, separate from the granular sludge, and including directing theprimarily floc sludge overflow to the mainstream process.